The polyphenylene ethers are known and described in numerous publications including Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875 and Stamatoff U.S. Pat. Nos. 3,257,357 and 3,257,358. The high molecular weight polyphenylene ethers are high performance engineering thermoplastics possessing relatively high melt viscosities and softening points -- i.e., in excess of 275.degree.C., and are useful for many commercial applications requiring high temperature resistance including formation of films, fibers and molded articles.
Although they have the above-described desirable properties, it is also known that certain properties of the polyphenylene ether resins are undesirable for some commercial uses. For example, parts moled from the polyphenylene ethers are somewhat brittle due to poor impact strength. In addition, the relatively high melt viscosities and softening points are considered a disadvantage for many uses. Films and fibers can be formed from polyphenylene ether resins on a commercial scale using solution techniques, but melt processing is commercially unattractive because of the high temperatures required to soften the resin and the problems associated therewith such as instability, discoloration and the requirement for specially designed process equipment to operate at elevated temperatures. Molded articles can be formed by melt processing techniques, but, again, the high temperatures required are undesirable.
It is known in the art that properties of the polyphenylene ether resins can be materially altered by blending them with other resins. For example, one method for improving the melt processability of the polyphenylene ethers is disclosed in a commonly-assigned assigned patent, U.S. Pat. No. 3,379,792, incorporated herein by reference. According to this patent, flow properties of the polyphenylene ethers are improved by blending with from about 0.1 to 25 parts by weight of a polyamide. In another commonly-assigned patent, U.S. Pat. No. 3,361,851, a polyphenylene ether composition comprising a polyphenylene ether blended with a polyolefin is disclosed. The polyolefin is added to improve impact strength and resistance to aggressive solvents. In a third commonly-assigned patent, Cizek, U.S. Pat. No. 3,383,435, there are provided means for simultaneously improving the melt processability of the polyphenylene ether resins while simultaneously up-grading many properties of polystyrene resins. The invention of the Cizek patent is based upon the discovery that the polyphenylene ether resins and polystyrene resins, including modified polystyrene resins, are combinable in all proportions and result in compositions having many properties improved over those of either of the components.
One preferred embodiment of the Cizek patent is a composition comprising a high-impact, rubber reinforced polystyrene and a poly(2,6-dialkyl-1,4-phenylene)ether. This composition was preferred because it provides the aforementioned objectives of improving the melt-processability properties of the polyphenylene ether resin and provides the further advantage of improving impact resistance of parts molded from the blend. Furthermore, the Cizek composition of the polyphenylene ether and the high impact polystyrene could be custom-formulated to provide predetermined properties ranging between those of the polystyrene and those of the polyphenylene ether by controlling the ratio of the two polymers. The reason for this is that the blend exhibits a single set of thermodynamic properties rather than two distinct sets of properties -- i.e., one for each of the components of the blend as is typical with blends of prior art.
Another preferred embodiment of the Cizek patent is a composition comprising a diene rubber-containing interpolymer resin (ABS--16% ACN, 41% styrene, 43% butadiene units) and a poly(2,6-dimethyl-1,4-phenylene)ether. Such compositions (e.g., Example 11 of Cizek, U.S. Pat. No. 3,383,435) are shown to have somewhat enhanced resistance to organic environments, e.g., gasoline, acetone and hexane, although the data are somewhat variable. No impact strength data are given for such compositions, although, as will be shown hereinafter, a similar diene-containing interpolymer resin (25% ACN, 30% styrene, 45% butadiene units) provides compositions with poly(2,6-dimethyl-1,4-phenylene)ether which possess good, but not outstanding impact strengths over the entire range of composition ratios.
With respect to the preferred embodiments in the Cizek patent, it is believed that the impact resistance of the polyphenylene ethers is improved because of the diene rubber content in the high-impact polystyrene and in the diene rubber resin and, in this respect, the improvement in impact strength appears to be directly proportional to the diene rubber content of the polystyrene resin or the ABS resin, increasing concentrations of diene rubber resulting in increased impact strength. However, it has also been found -- as a disadvantage -- that the gloss of parts molded from the polyphenylene ether resin and the high impact polystyrene resin or the diene rubber resin is inversely proportional to the diene rubber content and that, therefore, as the diene rubber content is increased, gloss and surface appearance of the molded parts are decreased. Consequently, increasing the diene rubber content of the compositions results in increased impact strength, but with a sacrifice in surface appearance and gloss. Alternatively, reduction in diene rubber content such as by the use of unreinforced (crystal) polystyrene results in parts having good gloss, but at a sacrifice to impact strengths. Because both impact strength and gloss are commercially important properties in the manufacture of molded parts, although the preferred compositions of the Cizek patent provide the advantages noted above, it has been found difficult to provide compositions having both optimum impact strength and surface appearance.
In addition, as mentioned above, the polyphenylene ether - diene rubber interpolymer resin compositions of the Cizek patent provide improvements in resistance to aggressive organic solvents, but the need still exists for compositions with outstanding resistance to gasoline.
It has now been discovered that an acrylic resin-modified diene rubber-containing interpolymer resin, will impart unexpectedly high impact strengths and chemical resistance properties both to polyphenylene ether resins and compositions of polyphenylene ether resins and polystyrene resins. For example, a piece molded from a composition comprising 60 parts of polyphenylene ether resin and 40 parts of a poly(methyl methacrylate) modified butadiene resin containing interpolymerized acrylonitrile and styrene units (ABS) has an Izod impact strength of 9 ft.lbs./in. notch and when placed in a 1% strain jig and immersed in gasoline, no crazing or cracking occurred even after several hours. Furthermore, a composition of 50 parts of poly(2,6-dimethyl-1,4-phenylene) ether, 40 parts of a poly(methyl methacrylate) modified ABS resin and 10 parts of rubber modified high impact polystyrene resin can be molded into a part with an Izod impact strength of 9.2 ft.lbs. per inch notch and similar, excellent resistance to a gasoline environment. Such blends can also be reinforced with fibrous glass with the enhancement in physical properties and no loss of excellent resistance to gasoline environments. All such blends have higher impact strengths, greater tensile elongations and substantially improved resistance to organic solvent attack than the corresponding compositions of the prior art in which the diene rubber-containing resin is not modified by the acrylic resin. In addition the new compositions have unusually good resistance to distortion by heat.